Heretofore, optical image forming materials for a proof paper, a printout paper, an overlay film, and the like have been used in many photographic applications in the form of free radical photographs in which photosensitive portions are visualized by imagewise exposure.
In this regard, those methods in which various kinds of leuco dyes are color developed by radical oxidation to dyes corresponding thereto using photooxidizing agents are particularly effective. In these methods, color is formed on exposure to usual indoor light, sunlight or white light, even after dye images have been formed by exposure, due to the sensitivity of leuco dyes to light. Thus, several methods have been proposed in which fixing is carried out after image exposure. Of these, an optical image forming material is known in which a leuco dye and a photooxidizing agent are contained together in microcapsules, and a reducing agent is present outside the microcapsules. This arrangement allows the image recording material to be fixed by heat treatment after exposure as described in U.S. Pat. No. 4,962,009. The use of hydroquinone reducing agent is known to improve the storage stability after fixing of this type of optical image forming material, as described in JP-A-3-191341 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). However, these hydroquinone reducing agents are disadvantageous in background portions become color developed (fogged) during storage in the dark after fixing. This results in a reduction in contrast between images and the background portion (white portion) to thereby deteriorate quality and performance.
On the other hand, low temperature fixing type optical image forming materials have been proposed in which reducing agents are used in combination with compounds which lower the melting point of the reducing agents in order to lower the fixing temperature and decrease the fixing time (U.S. Pat. No. 4,929,530). However, this type of system also does not prevent color development (fogging) of the background portions during storage in the dark after fixing.